This invention relates generally to vehicle rearview mirror systems and, more particularly, to mirror systems in which at least one mirror position is stored in a memory device and may be recalled and the mirror driven to the stored position. The invention is particularly directed to a position transducer which monitors the position of the mirror as part of the vehicle memory mirror function.
A vehicle memory system includes an actuator that is capable of independently adjusting a reflective element in two different degrees of freedom. A controller includes a memory device for storing at least one mirror position which may be retrieved and the mirror driven to that position with respect to each of the degrees of freedom. In order to do so, it is necessary to provide positional feedback to the controller in order for the controller to know the position of the mirror with respect to each degree of freedom. Accordingly, the actuator also includes a pair of position transducers to monitor the position of the mirror with respect to such degrees of freedom. The position transducers may be linear position transducers which are movable with respect to an outer portion of the mirror opposite the motor driving the mirror with respect to that degree of freedom. Thus, although the mirror is moved in an arcuate motion, the position of the mirror is monitored as a linear movement of the linear position transducer.
One technique that has been proposed is to utilize a Hall-effect sensor. While such Hall-effect sensors operate reasonably well, they are relatively expensive for automotive applications and, therefore, add significant cost to a memory feature of the mirror system. Another approach is to provide a pair of spaced apart parallel conductive tracks typically arranged as a voltage divider and a brush mechanism spanning the traces. By suitable connection of such circuit to a controller, the position of the brush along the traces may be monitored as a signal produced by the traces, which varies as a function of the brush on the traces. Therefore, by providing a suitable coupler between the brush and the reflective element, the position of the reflective element with respect to a degree of freedom can be monitored by the signal supplied to the controller.
In one such linear position transducer, the coupler is an elongated rod which rides in a cylindrical cavity. A first end of the rod is joined for movement with the reflective element and the opposite end is enlarged and provided with an arcuate outer surface which is rotatably slidably guided by the walls of the cavity. A mounting member for the brush projects through an opening in the cavity wall and thereby moves the brush along an adjacent circuit board. In addition to being relatively expensive to produce, the relatively large separation distance between the brush and the rod causes the relative spacing between the brush and the circuit board to be varied as the elongated member rotates within the cavity. This makes spacing between the cavity and circuit board critical and requires the brush to be capable of accommodating substantial movement between its support and the circuit board while maintaining acceptable contact pressure with the resistive traces.